One common approach used to drive a motor in both directions involves the use of an H-bridge. So called because the driver is made up of four switching devices with the load (in your case the motor) bridging across the middle to form the "H" pattern.

The h-bridge driver has two control lines. One control line enables and disables the motor while the other control line allows you to select the direction either clockwise or counter-clockwise.

yes that method works but i heard it wasnt always the bestway, I might have misread them but its seems it will work in theory.
anyone kno what im talking about jump in plz...I might have just read something wrong..thx l8er

you mentioned the use of an electric motor, but you didn't specify whether it's AC or DC and at what voltage you intend to use. then members maybe can draw up something for you like the H-bridge as suggested by "hgmjr".

Features: Shaft Diameter suits the various gears and cogs found in the value pack P-9040 Assorted Gear Pack.

with that type of power would i need anything else?? obviously i need wiring, batteries and that 3 way switch watever ever it is but do i need resistors, chip, some sort of management..? anything at all?

so u want to use the H-bridge circuit...an EMF is the ElectroMagnetic Field. All electric motors have 1 of course. Moz said he could draw u a circuit but i think ill give it a try as well. Go with moz's since i havent made many circuits and mine will probly contain a couple errors if it even works lol ...hope this clears things up...l8er

am attaching the circuit drawing of the relay switch and the H bridge.

the relay control may look complicated but it has a good working principle.

the H bridge design is basic with the use of PNP & NPN transistors. the high side drivers Q1 & 2 are PNPs w/c acts as your current source for the motor. PNPs, P Fets & P Mosfets are good providers of current source. the low side drivers Q3 & 4 are NPNs w/c acts as your current sink for the motor. NPNs, N Fets, & N Mosfets are very efficient in this regard.

the Mosfets could have been my choice however due to high efficiency, but due to high trigger it would need a higher supply than your present supply. the 12v can still be used but another design has to be made like a cleaver circuit which would make things more complicated.

for cost consideration you can use NPNs for the high & low side drivers. PNPs cost more that NPNs.

the 2N6121 & 2N6124 can easily handle your 300ma motor (unloaded). if loaded you motor can draw as much as 2.5x your unloaded state.

You can also use 2 single pole relays to get forward-reverse control and the stop function happens automatically. Also the single pole dealy elliminates the possibilty of a short happening if the forward and reverse buttons are pressed at the same time ( the so called dis-allowed state).

This is a simple way of doing this. Sorry that it's hand drawn, but this would be an automatic system: Push either button, the limit switch will stop it when it reaches end of travel. Normally closed R & F aux-contacts act as interlocks to prevent R & F contactors from acting simultaneously. If I were building this for a practical device, I would use a manufactured reversing contactor that has a mechanical interlock as well.

to get your pic attached make sure you save it as a GIF. or something along those lines. I think jpeg will work as well but bitmap wont. Just open your scan in paint and hit "save as" then click GIF under the bar with file name. then just browse with the uploading mod on this forum or use a free one such as www.imageshack.us
You might know most of this but it never hurts to explain in detail ...thx l8er

Originally posted by Nettron@Mar 6 2005, 09:04 AMYou can also use 2 single pole relays to get forward-reverse control and the stop function happens automatically. Also the single pole dealy elliminates the possibilty of a short happening if the forward and reverse buttons are pressed at the same time ( the so called dis-allowed state).

[post=5885]Quoted post[/post]​

Click to expand...

hi

won't arcing occur when you throw the motor into reverse or vice versa?

won't arcing occur when you throw the motor into reverse or vice versa?

Click to expand...

Yes arcing is inevitable but you can help cut down on it by adding a damper capacitor across the motor terminals, left that out in the schematic for clarity along with the reverse biased diodes across the relay coils.

Ive used this same relay scheme in a motor control project via the parallel port a few years ago, actually heres the entire schematic for the project for those interested.

But to cut down on circuit complexity ( and PC board realestate) it'd prolly be better to go with a commercially available H-bridge IC such as a LMD18200.